As is well known in the wireless data communications arts, a common trade-off in the design of communication systems is performance versus bandwidth. That is, various aspects of communication performance can be improved at the expense of increased radio frequency (RF) bandwidth. One very important factor contributing to the performance of a communication system is the “quality” of the data channels used in the system. As is well known, data reception errors can be caused by the introduction of noise and interference during data transmissions across a channel. Signal interference distorts signals and their associated data during transmissions over the channel. A source of such noise and interference is radio-frequency interference (RFI) such as multi-path fading, multiple-access interference, and hostile jamming. Channel quality depends largely on the amount of noise and interference that exists on a channel relative to the strength of the signal levels of the channel. A channel that has a small amount of noise relative to the strength of the signals has high channel quality. Conversely, a channel that has a large amount of noise relative to the signal levels has low channel quality. Channel quality is typically measured in terms of the signal-to-noise (SNR) or Es/No (i.e., ratio of signal energy to noise energy) of a channel.
A wireless communication system can be properly designed to operate reliably in the presence of various types of noise and radio-frequency interference. For example, signals with very large RF bandwidths can be generated using a method known as adaptive frequency hopping (AFH) in which the carrier frequency of a digital communication signal is adaptively changed, or “hopped,” over a wide range of frequencies. One such AFH digital communication system is the Bluetooth™ protocol system that facilitates the transport of data between Bluetooth devices. Bluetooth technology is described in more detail in a specification published by the Bluetooth Special Interest Group (SIG), entitled “Specification of the Bluetooth System, version 1.2”, electronically available to the public via the well-known Internet at <http://www.Bluetooth.com>, published on Nov. 5, 2003, referred to herein as the “Bluetooth Specification” and is incorporated herein by reference in its entirety for its teachings on Bluetooth flow control, signals, devices and communication protocols and schemes. As used herein, “Bluetooth device,” “Bluetooth communication system” or any variation thereof refer to a device or system operating according to the Bluetooth™ protocol.
As described in more detail in the above-incorporated related applications, and in the incorporated Bluetooth Specification, Bluetooth communication systems use a frequency-hopping spread spectrum (FHSS) scheme when communicating between master and slave devices. In accordance with this frequency hopping spread spectrum scheme, frequencies are switched during data transmissions. Frequency hopping is performed in accordance with specified frequency-hopping algorithms so that devices can independently determine the correct frequency-hopping sequences (i.e., ordered lists of frequencies, sometimes referred to as “hop-sets”). In one example, pseudo-random FH sequences are independently determined by slave devices using their associated master device address and clock information.
Although the FH sequence associated with each Bluetooth master device is unique, piconets operating within close proximity can interfere with one another due to the relatively small number of independent channels used by the Bluetooth devices. In addition, channel noise and interference can be caused by a number of non-Bluetooth devices operating within close proximity to the Bluetooth devices. For example, as described in the above-incorporated related applications, an 802.11 protocol device operating within close proximity to a Bluetooth device can cause undesirable RF interference rendering one or more of the channels in the Bluetooth device's hop-set unusable. As is well known, the various IEEE 802.11 communication protocols (referred to hereinafter as “802.11”) are global standards for radio communications operating at 2.4 GHz radio frequencies. One exemplary well-known 802.11 communications protocol is the IEEE 802.11b protocol (referred to hereinafter as “802.11b”). The 802.11b protocol allows 802.11b devices (i.e., those that comply with the 802.11b standard) to operate at high data transmission rates (e.g., 11 Mbps). The 802.11b protocol is particularly useful in implementing Wireless Local Area Networks (WLANs). Devices complying with the 802.11b standard are described in more detail in a standard produced by the IEEE 802 Working Group, entitled “IEEE Std 802.11b-1999”, electronically available to the public via the well-known Internet at <http://standards.ieee.org>, referred to herein as the “802.11b Specification,” and is hereby incorporated herein by reference in its entirety for its teachings on 802.11b flow control, signals, devices and communication protocols and schemes. Another exemplary IEEE 802.11 communications protocol is the newly emerging IEEE 802.11g.
As noted above, one technique that may be used in solving interference problems is AFH. The purpose of AFH is to allow Bluetooth devices to improve their immunity to interference while allowing them to avoid causing interference to other devices in the Industrial, Scientific, and Medical (ISM) 2.4 GHz band. The basic principle is that Bluetooth channels are classified into two categories, used and unused, where used channels are part of the hopping sequence and unused channels are replaced by used channels in a pseudo-random manner in the hopping sequence. This classification mechanism allows for the Bluetooth devices to use 79 or fewer channels required in the incorporated Bluetooth Specification. Note that, in the United States, at least 75 channels (MHz) were required until 2002 when the FCC changed its regulations. The current minimum number of channels in the United States is 15, although there are other places (such as Europe) that require at least 20 channels. Hence, the minimum number of channels allowed by the incorporated Bluetooth Specification, NMIN, is 20.
An exemplary AFH Hopping Sequence follows. As an example, imagine that Bluetooth uses 10 channels (0 through 9). If all channels were “good,” a hopping pattern might be as follows:                4 6 1 7 5 3 9 3 4 1 2 1 6 5 3 8 6 1 0 3 8 4 0 2Now, if channels 6 and 7 were determined to be “bad,” the hopping pattern would appear as follows:        4 x 1 x 5 3 9 3 4 1 2 1 x 5 3 8 x 1 0 3 8 4 0 2In each case the value of “x” would be pseudo-randomly selected from the other 8 valid channels (0-5 and 8-9). Then, the new hopping sequence, after substitution, would appear as follows:        4 5 1 9 5 3 9 3 4 1 2 1 1 5 3 8 0 1 0 3 8 4 0 2        
The incorporated Bluetooth Specification defines the aspects of AFH that are necessary to ensure interoperability. This includes the hopping kernel, baseband behavior, Link Manager Protocol (LMP) commands, and Host Controller Interface (HCI) commands and events required to change and configure the hopping sequences. The Bluetooth Specification also defines a mechanism that allows a slave to report channel classification information to a master. However, the Bluetooth Specification does not define or describe any specific requirements of the channel assessment mechanism. Channel assessment is left to the innovation of the various chipset and end product manufacturers.
As described above, “channel assessment” can be implemented as an algorithm that is used by a Bluetooth device to determine a channel map of which channels are good and which are bad within the 2.4 GHz ISM band. This channel map can then be used for Adaptive Frequency Hopping (AFH) or proprietary coexistence techniques such as channel avoidance. For example, the channel map can be used to determine which channels are “used” (i.e., the “good” channels from the channel map), and which are “unused” (i.e., the “bad” channels from the channel map).
At present, channel assessment algorithms have used either active measurements (e.g., bit error rate, or packet error rate) or passive measurements (e.g., Received Signal Strength Indication (RSSI) measurement scan of the ISM band) in generating the channel maps. Disadvantageously, when using either passive or active measurements, the accuracy of the measurements depends on a number of factors including: the duty cycle of the interferer, the number of interferers, the number of samples used, etc. In general, these techniques are designed to provide an accurate estimate of the interference. However, in the end, the result is only a guess of what the interference profile truly looks like. Therefore, using these techniques, the interference profile will never be 100% accurate.
Therefore, a need exists for a method and apparatus that estimates and detects the presence of RF interference in a data channel. The data channel may have been previously determined by an AFH scheme to be “disallowed” (i.e., exhibited bad channel conditions), or it may be a channel within a frequency hop-set. The interference detection apparatus and method should be amenable for use in any communication system where the presence of intermittent interference needs to be detected.